Method and device for processing a moving production part, particularly a vehicle body

ABSTRACT

A method for processing a moving workpiece ( 1 ), in particular a vehicle body ( 1 ) which is moved using of a conveyor belt ( 10 ). A processing tool ( 5 ) is used which is attached to the hand ( 12 ) of a robot ( 7 ) and comprises a sensor system ( 18 ) which is permanently connected to the processing tool ( 5 ) and has at least one sensor ( 19 ). During the processing, the processing tool ( 5 ) follows the moving workpiece. This following movement is based on a closed-loop control process in which the processing tool ( 5 ) is oriented periodically towards reference areas ( 9 ) of the moving workpiece ( 1 ) using measured data of the sensor system ( 18 ). The measured data of the sensor system ( 18 ) is compared with setpoint data which is generated within the scope of a set up phase (I) of the processing tool ( 5 ), and a movement vector of the processing tool ( 5 ) is calculated from the difference between the measured values and setpoint data using a Jacobi matrix calculated within the scope of the set up phase, the processing tool ( 5 ) being moved by an amount equal to said movement vector. This process is repeated in a control loop.

The invention relates to a method for processing a moving workpiece, inparticular a vehicle body which is moved by means of a conveyor belt,according to the preamble of claim 1, such as is disclosed, for example,in DE 195 20 582 C1. Furthermore, the invention relates to a processingsystem for carrying out this method.

In the large-scale series production of motor vehicles, in particular inthe (final) assembly, continuously moving conveyor belts on whichvehicle bodies are fed to successive processing and assembly stationsare frequently used. At these processing and assembly stations, thevehicle bodies are typically removed from the conveyor belt and movedinto clocked stations so that the actual processing and assemblyoperations can be carried out on a fixed vehicle body. Each junctionbetween the continuously conveying means and a clocked station requiresacceleration sections and, under certain circumstances, buffers, whichrequires an increased amount of space. Furthermore, it is very costly tointegrate the processing or assembly station which can be automated intoan existing, continuously feeding assembly line because this requiresthe conveyor belt to be divided.

For this reason there is a keen interest in carrying out automated (i.e.robot-guided) processing and assembly operations directly on the movingobject. However, this often involves the difficulty that a processing orassembly robot which is used in such a context has to be coupled to theforward feed movement of the conveyor belt in order to synchronize therobot-guide as a processing or mounting tool with the moving vehiclebody. The greater the precision requirements made of the processing andassembly operations the greater the precision required of this coupling.

Such a synchronization may be achieved, for example, by mechanicallycoupling the processing or assembly robot to the conveyor belt. U.S.Pat. No. 3,283,918 discloses an assembly system in which the robot ismade to follow the assembly belt in synchronism with the belt as theprogrammed work is carried out using a mechanical device. In order tobring about synchronous running between the industrial robot and theworkpiece, in each case a laterally protruding driving pin, to which theindustrial robot is coupled, is arranged on each of the actualworkpieces moved on the conveyor belt or on a workpiece carrier. It is adisadvantage here that despite the synchronous running on both sides,which is brought about by the mechanical coupling between the industrialrobot and the workpiece, relative movement still always occurres betweenthe industrial robot and the workpiece and these prevent a preciseworking operation. These inaccuracies add up to relative movementoffsets which exceed the positional correspondence which is necessary ortolerable for a mechanized joining, processing or welding operation.

On the other hand, DE 195 20 582 C1, which forms a generic type,discloses an arrangement for synchronizing a robot with an assembly beltby means of closed-loop controlled equipment. In this system, a relativeposition closed-loop controller with a measuring device which candetermine, within a short compensation section, the position of a driverwhich is carried along by the workpiece, is provided on the assemblyrobot in this system. As a result, a highly relative precision can beachieved between the assembly robot and the moving workpiece. Adisadvantage with this synchronization of the robot with respect to theconveyor belt by means of closed-loop controlled equipment is thatposition information is acquired from the passing workpiece using asingle measurement and said information is then extrapolated usingfurther information (such as speed of the belt and forward feeddirection) to the assembly time. In the actual contact situation thereis then only indirect position information available, which can lead toincreased inaccuracies and, for example, in the case of an unexpectedshutdown of the belt, can lead to an increased requirement forsynchronization with the surrounding open-loop control system.

The invention is thus based on the object of developing the known methodfor robot-supported processing of a moving workpiece to the effect thata relative position of a robot-guided processing tool with respect tothe moving workpiece, as far as the execution of the actual processingtask, can be set and maintained by controlled processing. The inventionis also based on the object of proposing a processing system which issuitable for carrying out the method.

The object is achieved according to the invention by means of featuresof claims 1 and 6.

According to the invention, the robot-guided processing tool is providedwith a sensor system which is permanently connected to the processingtool. The processing tool is firstly moved under the control of a robotinto what is referred to as a “proximity position” (permanentlyprogrammed and independent of the current position of the workpiece inthe working space of the robot) with respect to the workpiece. Startingfrom this proximity position, a closed-loop control process is runthrough, in the course of which the processing tool is moved into whatis referred to as a “working position” in which the processing tooland/or an add-on part which is held in the processing tool is orientedin a precisely positioned fashion with respect to the workpiece. In thecourse of the closed-loop control process, (actual) measured values ofselected reference areas are generated on the workpiece and/or on theadd-on part by the sensor system, and these (actual) measured values arecompared with (setpoint) measured values which have been generated in apreceding setup phase. The processing tool is then moved by an amountequal to a movement vector (comprising linear movements and/orrotations) which vector is calculated from a difference between the(actual) and (setpoint) measured values using what is referred to as a“Jacobi matrix” (or “sensitivity matrix”). Both the (setpoint) measuredvalues and the Jacobi matrix are determined within the scope of a setupphase, preceding the actual positioning and mounting process, within thescope of which the processing tool is trained to the specific mountingtask (i.e. a specific combination of processing tool, sensor system,vehicle body type and type and installation position of the add-on partto be used).

“Processing” is intended to be understood here as referring to anyprocessing, mounting or measuring operations which are to be carried outon the moving object. In particular, the term “processing” is to beunderstood as comprising any joining processes on the moving object(welding operations in the body shell phase, application of adhesive inthe final assembly phase . . . ), mounting processes (installation ofwindshields, roof modules etc. in the vehicle assembly phase etc.) whichare synchronous with the belt and quality assurance measures(measurement and testing equipment using the production cycle) whichaccompany the processes.

In the course of the closed-loop control process described above, theprocessing tool is oriented in the desired working position with respectto the moving workpiece. Periodic (re-)orientation of the processingtool with respect to the workpiece is carried out by periodicallyrepeating the closed-loop control process so that the processing tool“follows” the moving workpiece. During this following process insynchronism with the belt, various processing and/or mounting operationscan be carried out on the moving workpiece by the processing tool, andat any time during these processing or mounting operations it ispossible to ensure that the processing tool is oriented in a preciselypositioned fashion with respect to the workpiece.

No (absolute) information about the instantaneous speed of the assemblybelt, the position and orientation of the moving workpiece in theworking space of the robot etc. is necessary for this purpose. Themethod according to the invention is in fact based on relativemeasurements of the sensor system, in the scope of which information(stored in the setup phase) relating to the closed-loop control processis restored, said information corresponding to a set of (setpoint)measured values of the sensor system.

Since no absolute measurements whatsoever are required to carry out themethod, the sensors used do not need to be calibrated either. Inparticular, it is possible to dispense with an internal metriccalibration of the sensors since the sensors which are used no longer“measure” but merely react to a monotonous incremental movement of therobot with a monotonous change in its sensor signal. This means, forexample, that, when a television camera or CCD camera is used as asensor, the camera-internal lens distortions do not have to becompensated and that when a triangulation sensor is used, the precisemetric calculation of distance values is dispensed with. Furthermore,there is no need for external metric calibration of the sensors. Thismeans that the position of the sensors with respect to the working spaceof the robot or the coordinate system of the robot's hand does not needto be determined in order to be able to calculate suitable correctionmovements. The sensors merely have to be attached to the processing toolin such a way that they are at all capable of sensing suitable measureddata of the reference areas on the vehicle body and/or of an add-on partin their capture range.

The result of the following of the path of the moving workpiece is alsoindependent of the absolute positioning accuracy of the robot used andthe knowledge about the movement sequence of the conveyor belt sincepossible inaccuracies of the robot and/or changes in the speed of thebelt when the working position is periodically moved to or re-adjustedare compensated. Owing to the resulting short error chains it ispossible to achieve a very high repetition accuracy when following thepath.

The number of degrees of positioning freedom of the processing tool withrespect to the moving workpiece which can be compensated with the methodaccording to the invention is freely selectable and only depends on theconfiguration of the sensor system. The number of sensors used can alsobe freely selected. The number of sensor information items madeavailable merely has to be equal to or larger than the number of degreesof freedom to be closed-loop controlled. In particular, a relativelylarge number of sensors can be provided and the redundant sensorinformation can be used in order, for example, to sense better shapingerrors in the workpiece areas under consideration or to improve theaccuracy of the positioning process. Finally, sensor information can beused from different, preferably contact-free sources (for example acombination of CCD cameras, optical gap sensors and triangulationdistance measuring sensors). As a result, by using suitable sensors itis possible to take into account the measurement results of differentquality-related variables (gap dimensions between the workpiece and anadd-on part held in the processing workpiece, junction dimensions, depthdimensions). The method according to the invention can be adapted veryeasily to new problems since only the means for acquiring andconditioning the sensor data has to be adapted but not the closed-loopcontrolling system core.

Further advantageous embodiments of the invention can be found in thesubclaims. The invention is explained in more detail below withreference to an exemplary embodiment which is illustrated in thedrawings, in which:

FIG. 1 shows a schematic plan view of a processing system for processinga vehicle body which is moved on a conveyor belt, in different processphases:

FIG. 1 a feeding in of the vehicle body,

FIG. 1 b processing the vehicle body (bonding of a roof module);

FIG. 2 shows schematic sectional views of the processing system and ofthe moving vehicle body in FIG. 1 in different process phases:

FIG. 2 a: working position of the processing tool with respect to themoving vehicle body;

FIG. 2 b: proximity position of the processing tool with respect to themoving vehicle body, and

FIG. 3 shows a schematic illustration of the movement path of theprocessing tool during the execution of mounting steps in FIGS. 1 and 2.

FIG. 1 a shows a plan view of a processing system 4 in which roofmodules 3 are bonded into roof openings 2 in vehicle bodies 1. Vehiclebodies 1 are fed to the processing system 4 on a conveyor belt 10 andare continuously conveyed on the conveyor belt 10 through the workingspace 6 of the processing system 4 (direction of arrow 11) during themounting of the roof module. Each roof module 3 is fed in by a robot 7and is provided in its edge region with a bonding agent run 29 by meansof which the roof module 3 is connected to the roof opening 2 in thevehicle body 1.

In order to be able to mount the roof module 3, by controlledprocessing, in the vehicle body 1 which is moved on the conveyor belt10, the roof module 3 must be oriented in a precise positioned fashion(in terms of position and angular attitude) with respect to the roofopening 2 in the moving vehicle body 1, in particular a gap 21 which isprovided between the roof module 3 and the adjacent roof areas 9 musthave a dimension which is as uniform as possible (see FIG. 2 a). Theadjacent roof areas 9 form here what is referred to as a reference areafor orienting the roof module 3 with respect to the vehicle body 1. Thisrelative orientation between the roof module 3 and roof opening 2 mustbe retained during the mounting-related process steps, i.e. the roofmodule 3 must be held with this relative orientation with respect to theroof opening 2 (or pressed onto the roof opening 2) until the bondingagent gels, in order to obtain the desired gap dimension.

The mounting of the roof module 3 in the vehicle body 1 is carried outusing a processing tool 5 which is guided by the industrial robot 7 andwhich places the roof module 3 on the moving vehicle body 1 andpositions it precisely with respect to the roof opening 2 in the vehiclebody 1. An open-loop control system 20 is provided for controlling therobot 7 and the processing tool 5 in terms of position and movement. Theprocessing tool 5 is attached to the hand 12 of the industrial robot 7and comprises a frame 13 to which a securing device 14 is attached andby means of which the roof module 3 can be held in a well definedposition. In the present exemplary embodiment, the securing device isformed by a plurality of under-pressure suction cups which engage on theupper side 22 of the roof module 3.

In order to measure the position and orientation of the roof module 3,secured in the processing tool 5, with respect to the moving vehiclebody 1, the processing tool 5 is provided with a sensor system 18 with aplurality of sensors 19 which are rigidly connected to the frame 13 ofthe processing tool 5, and they thus form one structural unit with theprocessing tool 5. The sensors 19 are used to determine join dimensions,gap dimensions and depth dimensions between the reference areas 9 of theroof opening 2 and the adjacent reference areas 17 of the roof module 3.Using this sensor system 18, the roof module 3 which is held in theprocessing tool 5 is oriented, as described below, with respect to theroof opening 2 in the vehicle body 1 in an iterative closed-loop controlprocess and held in this orientation during the entire mounting process.

If the processing system 5 is to be set to a new processing task, forexample to the mounting of a roof module in a new type of vehicle, whatis referred to as a setup phase, in which the processing tool 5 isconfigured, must be firstly run through. In the process, a securingdevice 14 which is adapted to the roof module 3 to be mounted, a frame13 which is suitably configured and a sensor system 18 withcorresponding sensors 19 are selected and assembled. After this, thesensor system 18 of the processing tool 5 is “trained” by (setpoint)measured values of the sensor system 18 being recorded, as describedbelow in section I, on a “master” vehicle body 1′ which is held in afixed fashion and a “master” roof module 3′, and by programming the pathsections, to be run through in an open-loop controlled fashion, of amovement path 16 of the robot 7. After this setup phase has finished,the processing system 4 which is configured and calibrated in this wayis ready for series-production use, during which what is referred to asa working phase is run through for each vehicle body 1 which is fed to aworking space 6 of the processing system 4, in which working phase, asdescribed below in section II, an associated roof module 3 is positionedand attached in the roof opening 2 of the vehicle body 1.

I. Setup Phase of the Processing Tool 5:

In order to carry out a new reset processing task, in a first step asensor system 18 which is adapted to the processing task is firstlyselected for the processing tool 5 and attached, together with thesecuring device 14, to the frame 13. The processing tool 5 which isassembled in this way is attached to the robot's hand 12. The securingdevice 14 is then equipped with a (“master”) roof module 3′ and oriented(manually or interactively) with respect to a (“master”) vehicle body 1′secured in a fixed fashion in the working space 6, in such a way thatthe (“master”) roof module 3′ is oriented in an “optimum” way withrespect to the (“master”) vehicle body 1, and this relative position ofthe (“master”) roof module 3′ with respect to the (“master”) vehiclebody 1′ is illustrated in FIG. 2 a. Such “optimum” orientation may bedefined, for example, by the gap 21 between the (“master”) roof module3′ and the (“master”) vehicle body 1′ being as uniform as possible, orthe gap 21 assuming specific values in specific regions. The relativeposition which is assumed here by the processing tool 5 with respect tothe (“master”) vehicle body 1′ is designated below as “working position”23.

The number and position of the sensors 19 in the sensor system 18 isselected such that the sensors 19 are directed towards suitable areas 9,17, particularly important for the “optimum” orientation, of the(“master”) vehicle body 1′ and of the (“master”) roof module 3′. In theexemplary embodiment in FIG. 2 a, two optical sensors 19 which measureover an area and which are both directed towards the edges 33, 34,adjacent to one another, of the (“master”) vehicle body 1′ and of the(“master”) roof module 3′ are shown symbolically. The profiles of theedges 33, 34 in the image field of the sensors 19 and the dimensions ofthe gap 21 are calculated in the evaluation unit 26 from images recordedby the sensors. In addition to these gap measurement sensors, it ispossible to provide further sensors which, for example, measure a(depth) distance between (“master”) vehicle body 1′ and (“master”) roofmodule.

The processing tool 5 with the sensor system 18 and with the (“master”)roof module 3′ held in the securing device 14 is then “trained”, usingthe robot 7, to the working position 23 (set by means of the manual orinteractive orientation and assumed in the illustration in FIG. 2 a)with respect to the (“master”) vehicle body 1′. In the process, measuredvalues of all the sensors 19 are firstly recorded in the workingposition 23 and stored as “setpoint measured values” in an evaluationunit 26 of the sensor system 18, and this sensor evaluation unit 26 isexpediently integrated into the control system 20 of the robot 7. Then,starting from the working position 23, the position of the processingtool 5 and of the (“master”) roof module 3′, which is held therein, withrespect to the (“master”) vehicle body 1′ is changed systematicallyalong known movement paths, indicated by arrows in FIG. 2 a, using therobot 7, and as a rule these are incremental movements of the robot 7 inits degrees of freedom. The changes which occur in the measured valuesin the sensors 19 in the process are recorded (completely or partially).What is referred to as a “Jacobi matrix” (sensitivity matrix) iscalculated from this sensor information in a known fashion, said matrixdescribing the relationship between the incremental movements of therobot 7 and the changes which occur in the sensor measured values in theprocess. The method for determining the Jacobi matrix is described, forexample, in “A tutorial on visual servo control” by S. Hutchinson, G.Hager and P. Corke, IEEE Transactions on Robotics and Automation 12(5),October 1996, pages 651-670. In this article, there is also adescription of the requirements made of the movement paths and themeasuring environment (constancy, monotony, . . . ) which have to befulfilled in order to obtain a valid Jacobi matrix. The incrementalmovements are selected in such a way that during this setup processcollisions cannot occur between the processing tool 5 or the (“master”)roof module 3+ and the (“master”) vehicle body 1′.

The Jacobi matrix which is generated in the setup phase is stored,together with the “setpoint measured values” in the evaluation unit 26of the sensor system 18, and this data forms the basis for the laterpositioning process, to be run through in a closed-loop controlledfashion, of the processing tool 5 with respect to the moving vehiclebody 1 and the high-precision, closed-loop controlled movement by theworking tool 5 as it follows the vehicle body 1 in the working phase(see section II below).

Furthermore, a movement path 16 of the robot's hand 12 (and thus of theprocessing tool 5) is generated in the setup phase and run through in anopen-loop controlled fashion in the later working phase II. Thismovement path 16 is represented schematically in FIG. 3. The startingpoint of the movement path 16 is formed by what is referred to as a“return movement position” 30 which is selected such that there is norisk of collisions occurring between the processing tool 5 or the roofmodule 3 held therein and the vehicle bodies 1 which are moved on theconveyor belt 10. This return movement position 30 may correspond, forexample, to an equipping station (not illustrated in the figures) inwhich the roof module 3 is held by the mounting tool 5 and in whichbonding agent runs 29 are applied to selected areas 28 of the undersideof the roof module using a bonding agent-applying robot (not shown inFIGS. 1 a and 1 b), and.

Starting from this return movement position 30, the movement path 16comprises the following separate sections:

-   -   A-1 The processing tool 5 with inserted roof module 3 is moved,        on a path A-1 which is to be run through in an open-loop        controlled fashion, from the return movement position 30 into a        permanently predefined, so-called “proximity position” 27 which        is selected such that all the individual sensors 19 of the        sensor system 18 can sense valid measured values of the        respective area 9, 17 of the roof module 3 and/or of the vehicle        body 1, while at the same time it is ensured that collisions        between the processing tool 5 or the roof module 3 and the        vehicle body 1 cannot occur (see FIG. 2 b).    -   A-2 The processing tool 5 with inserted roof module 3 is moved,        on a path A-2 which is to be run through in a closed-loop        controlled fashion in the later working phase, from the        proximity position 27 into the working position 23 (“trained” as        described above) in which the roof module 3 which is held in the        processing tool 5 is oriented in a precisely positioned and        angled fashion with respect to the roof opening 2 in the vehicle        body 1. What happens in particular during this process step to        be run through in a closed-loop controlled fashion is described        below (in II working phase).    -   B Now there is the actual processing operation, during which the        roof module 3 which is held in the processing tool 5 is pressed        into the roof opening 2 with a predefined pressure and held in        this position until the bonding agent 29 gels or cures, and        during this time the robot 7 periodically runs through a        closed-loop control process, as a result of which the processing        tool 5 remains oriented in the relative position (found as a        result of the closed-loop control process A-2) with respect to        the moving vehicle body 1.    -   C If the mounting process has finished, the control system 20 of        the robot 7 outputs the signal which causes the processing tool        5 to stop following the moving vehicle body 1 in an oriented        fashion. The processing tool 5 is then moved back under robot        control into the return movement position 30.

The movement path 16, generated within the scope of the setup phase, ofthe processing tool 5 is thus composed of two sections A-1 and C whichare to be run through in an open-loop controlled fashion, and twosections A-2 and B which are to be run through in a closed-loopcontrolled fashion. Steps A-1 and C can be input interactively duringthe training phase of the processing tool 5 or they can be stored in theform of a program (generated off-line) in the open-loop control system20 of the robot 7.

II. Working Phase

In the working phase, vehicles bodies 1 are carried sequentially throughthe working space 6 of the processing system 4 on the conveyor belt 10,and in each of these moving vehicle bodies I a roof module 3, providedwith a bonding agent run 29, is positioned precisely with respect to theroof opening 2 by means of the processing system 4 and using themovement path 16 trained in the setup phase I, and said roof module 3 isinstalled in the moving vehicle body 1 with this relative orientation.

Movement Path Section A-1 (Proximity Phase):

While the new vehicle body 1 is being fed in, the processing tool 5 isin the return movement position 30 and in said position it picks up aroof module 3 which is to be provided with a bonding agent 29 and is tobe mounted (see FIG. 1 a). As soon as the new vehicle body 1 has beenmoved into the working space 6 (and has moved through, for example, aphotoelectric barrier in the process), the control system 20 of therobot 7 receives a signal which triggers the movement path section A-1.The processing tool 5 with inserted roof module 3 is moved here in anopen-loop controlled fashion into the (spatially fixed) proximityposition 27 in FIG. 2 b which, as mentioned above, has been selected insuch a way that the roof opening 2 (or the reference areas 9) of themoving vehicle body 1 are located in the capture area of the sensors 19of the processing tool 5 irrespective of the precise position of thevehicle body on the conveyor belt 10.

Movement Path Section A-2 (Positioning Phase of the Processing Tool 5):

Starting from this proximity position 27, a positioning phase (pathsection A-2 in FIG. 3) of the processing tool 5 is run through, in thescope of which the roof module 3 which is held in the processing tool 5is moved into the working position 23 (trained during the training phaseI) with respect to the moving vehicle body 1 and in the process orientedin a precisely positioned fashion with respect to the roof opening 2.For this purpose, measured values are recorded by the sensors 19 of thesensor system 18 in selected areas 9, 17 of the roof module 3 and of thevehicle body 1. A movement increment (movement vector) which reduces thedifference between the current (actual) sensor measured values and the(setpoint) sensor measured values is calculated using these measuredvalues and the Jacobi matrix determined in the setup phase. The roofmodule 3 which is held in the processing tool 5 is then moved and/orpivoted by this movement increment using the robot 7, and new (actual)sensor measured values are recorded during the ongoing movement.

This iterative measuring and movement process is repeated in a controlloop until the difference between the current (actual) and the end-at(setpoint) sensor measured values drops below a predefined faultmeasure, or until this difference no longer changes beyond a thresholdvalue which is specified in advance. The roof module 3 is then in theworking position 23 (illustrated in FIG. 2 a) with respect to thevehicle body 1 (within the scope of the accuracy predefined by the faultmeasure or threshold value).

The iterative minimization which is run through in this positioningphase A-2 compensates both inaccuracies in the vehicle body 1 in termsof its position and orientation on the conveyor belt 10 and possiblypresent shaping errors of the roof opening 2 of the vehicle body 1 (i.e.deviations from the (“master”) vehicle body 1′). At the same time,inaccuracies in the roof module 3 with respect to its position andorientation in the processing tool 5 and possibly present shaping errorsof the roof module 3 are compensated (i.e. deviations from the(“master”) roof module 3′). As a result of a periodic repetition of therecording of measured values and of the closed-loop control process, themovement of the vehicle body 1 in the working space 6 of the processorsystem 4 is furthermore compensated so that the robot-guided processingtool 5 “follows” the vehicle body 1. Such “following” of the vehiclebody 1 by the processing tool 5 by controlled processing merely requireschanges in the relative position between the vehicle body 1 and therobot 8 to take place more slowly than the measurement and closed-loopcontrol of the position of the sensor system 18 and processing tool 5(or robot's hand 12).

In the course of this iterative closed-loop control process A-2, theroof module 3 is fitted into the roof opening 2 in the vehicle body 1 inthe “optimum” way independently of the movement of the vehicle body 1.In order to detect and evaluate shaping errors of the roof module 3 andof the vehicle body 1 separately, it is possible to provide additionalsensors (i.e. not required for the actual positioning task) on theprocessing tool 5, the measured values of which sensors are usedexclusively or partially for sensing the shaping errors. Furthermore themeasured values of the individual sensors 19 can be provided withdifferent weighting factors in order to bring about a weightedoptimization of the position of the roof module 3 with respect to theroof opening 2 in the vehicle body 1.

An important property of the positioning phase A-2 is its independencefrom the accuracy of the robot: since the positioning process is basedon an iterative comparison between the (actual) measured values and(setpoint) measured values, any positioning inaccuracy of the robot 7 iscompensated immediately by the iterative control process.

Operation B (Attachment of the Roof Module 3 to the Vehicle Body 1):

In the working step B which now follows, the roof module 3 is connectedto the vehicle body 1. The processing tool 5 follows the moving vehiclebody 1 in a closed-loop controlled fashion in that the sensors 19periodically record, in continuation of the process step A-2, measuredvalues of the areas 9 on the vehicle body 1 in an iterative controlloop, and compare said values with the setpoint data stored in theevaluation unit 26, and if differences occur between the setpoint andthe actual values—which can be expected with a moving vehicle body 1—theposition of the robot's hand 12 is corrected in an analogous way to theclosed-loop control process described in A-2 in order to keep thesedifferences as small as possible.

In parallel with this closed-loop controlled following movement of themounting system 5 by the sensor system 18, the roof module 3 is thenheld in the desired relative position (corresponding to the workingposition 23) with respect to the roof opening 2, or pressed with apredefined (or closed-loop controlled) force onto the roof opening 2,using the securing device 14. When the gelling or hardening time of thebonding agent 29 has passed, the roof module 3 is released by thesecuring device 14.

Depending on the duration of the processing operation to be carried outin this operation B and on the forward feed speed of the conveyor belt10 it may be expedient not to hold the robot 7 in a fixed way but ratherto move it on a rail 15 running parallel to the conveying direction 11of the belt 10. The path movement of the robot 7 on the rail 15 is aclosed-loop controlled movement here and is thus not coupled to theforward feed of the conveyor belt 10. Irrespective of whether or not therobot 7 moves along with the conveyor belt 10, the orientation of theroof module 3 on the moving vehicle body 1 which accompanies the processis therefore carried out exclusively by the iterative closed-loopcontrol process described above, i.e. on the basis of the on-lineacquisition and evaluation of measurement data by the sensor system 18.For this reason, there is no need to couple the processing tool 5 to theconveyor belt 10 mechanically and the open-loop control system 20 of therobot 7 does not need to be interconnected to the open-loop control theconveyor belt in any way (electrical/electronic).

During the following phase B, a position control loop is advantageouslyrun through periodically at predefined (as short as possible) timeintervals in order to keep the tool 5 continuously oriented with respectto the roof opening 2. If this is not possible (because, for example,the tool 5 briefly has to be moved out of the roof area in order to makethis area accessible to further tools), a brief “dry run” can be carriedout by the robot's hand 12 during which the estimated forward feed ofthe vehicle body I is estimated.

Movement Path section C (Return Movement of the Processing Tool 5):

After the mounting of the roof module 3 has finished (see FIG. 1 b), theclosed-loop controlled following movement, which is described in sectionB and by means of which the processing tool 5 is coupled to theconveying movement of the vehicle body 1, is aborted. The processingtool 5 is moved back along the movement path C, under the control of therobot, into the return movement position 30 and equipped there with anew roof module 3.

When a new roof module 3 is picked up by the processing tool 5, thesensor system 18 can be used to ensure that the roof module 3 isoriented in a highly precise fashion in the processing tool 5. In thiscase, the processing system 5 is trained to a “pick-up position” in thecourse of a setup phase which proceeds in an analogous way to the setupphase described above in section I, said “pick-up” positioncorresponding to a predefined position/orientation of the processingtool 5 (and thus of the sensors 19 of the sensor system 18) with respectto the roof module 3. The roof module 3 is fed to the processing system4 in, for example, a workpiece carrier (not illustrated in the figures).A method, which can be automated, for removing a roof module from aworkpiece carrier in a precisely positioned fashion is described in (PCTpatent application, our file number P803860).

The highly precise orientation of the roof module 3 in the processingtool 5 is recommended in particular if the roof module 3 is moved alongin the equipping station (i.e. before the insertion into the movingvehicle body 1 described above) on an open-loop controlled path past abonding tool (for example a bonding robot) using the processing tool 5,said bonding tool applying the bonding agent run 29 to the desired areas28 of the roof module 3. In order to bond the roof module 3 in the roofopening 2 by controlled processing it is indispensable to ensure aprecise position of the bonding agent run 29 on the roof module 3, andthis in turn can be carried out with an acceptable amount of cost onlyif the roof module 3 is oriented in a highly precise fashion withrespect to the bonding tool during the application of the bonding agent,which can be ensured by high precision positioning of the roof module 3in the mounting tool 5. In this case, in the course of the working phaseII during the positioning phase A-2 (and the following phase B), theprocessing tool 5 must only be oriented with respect to the referenceareas 9 of the vehicle body 1, and the position of the reference area 17of the roof module 3 is known owing to the precisely positioned way inwhich the roof module 3 is held in the tool 5 so that the features nolonger need to be sensed during the working phase II.

Alternatively, the roof module 3 can be held “imprecisely” with respectto its position/orientation (i.e. without highly precise orientation ofthe tool 5 with respect to the roof module 3) in the processing tool 5.This is recommended, for example, in the cases in which the roof module3 is already provided with a bonding agent run 29 at the time when it ispicked up by the processing tool 5. In this case, in the course of theworking phase II during the positioning phase A-2 (and the followingphase B), measured data is sensed both by the roof module 3 and by thevehicle body 1 so that the relative position is conveyed. Owing to thisrelative positioning during the working phase II, the “imprecise”support of the roof module 3 in the tool 5 does not have any influenceat all on the positioning accuracy of the roof module 3 in the roofopening 2.

A TCP/IP interface, which permits a high data rate, is advantageouslyused in the present exemplary embodiment for the purpose of datacommunication between the different system components (evaluation unit26 of the sensor system 18 and of the control unit 20 of the robot 7).Such a high data rate is necessary in order to be able to carry outclosed-loop control of the entire system (sensor system/robots) with thelarge number of individual sensors 19 using the interpolation cycle ofthe robot 7 during the positioning and following phases A-2 and B whichare to be run through in a closed-loop controlled fashion.

As well as the mounting of roof modules in vehicle bodies, the methodcan be transferred to any other processing operations in which arobot-guided processing tool 5 is to be used to process a workpiece 1with high precision. In particular, the method is suitable for mountingfront windshields in moving vehicle bodies. “Robot-guided” processingtools are to be understood in the context of the present application ina quite general way as tools which are mounted on a multi-axlemanipulator, in particular a six-axle industrial robot 7.

1-8. (canceled)
 9. A method for processing a moving workpiece movedusing conveyor belt, a processing system for processing the workpiecehaving a processing tool attached to a hand of a robot, the processingsystem including a sensor system fixedly connected to the processingtool, the sensor system including at least one sensor, the methodcomprising the following steps: moving, during a positioning phase, thehand with the processing tool into a working position, the processingtool in the working position being oriented in a precisely positionedfashion with respect to a reference area of the workpiece moved on theconveyor belt; maintaining, during a subsequent processing phase, theprocessing tool oriented with respect to the reference area on theworkpiece; running through a periodically repeating, iterativeclosed-loop control process during the positioning phase and theprocessing phase, the closed-loop control process including: generatingan actual measured value of the reference area of the workpiece by theat least one sensor, comparing the actual measured value with a setpointmeasured value generated during a set up phase, calculating a movementvector of the hand from a difference between the actual measured valueand the setpoint measured value using a Jacobi matrix calculated duringthe set-up phase, and moving the processing tool using the movementvector.
 10. The method as recited in claim 9 wherein a TCP/IP interfaceis used for communication between a control system of the robot and anevaluation unit of the sensor system.
 11. The method as recited in claim9 wherein to position the processing tool with respect to differentvehicle body types or with respect to different reference areas of asame vehicle body type, the measured values of different individualsensors of the sensor system are used for closed-loop position control.12. The method as recited in claim 9 wherein the workpiece is a vehiclebody.
 13. The method as recited in claim 12 wherein the processing toolmounts a roof module in a roof opening in the vehicle body.
 14. Themethod as recited in claim 12 wherein the processing tool mounts awindshield in a front window opening in the vehicle body.
 15. Aprocessing system for processing a moving workpiece moved using aconveyor belt, the processing system comprising: a processing toolattached to a hand of a robot; a control system for controlling therobot and the processing tool; a sensor system having at least onesensor fixedly connected to the processing tool; and an evaluation unitfor evaluating measured values of the sensor system; the at least onesensor, during a positioning and processing phase, being directed towarda reference area of the moving workpiece, the processing tool capable ofbeing coupled in a contact-free fashion to a path movement of the movingworkpiece using measured values of the sensor system.
 16. The processingsystem as recited in claim 15 wherein the at least one sensor is anoncalibrated sensor.
 17. The processing system as recited in claim 16wherein the at least one sensor is an optical sensor measuring over anarea.
 18. The processing system as recited in claim 15 wherein the atleast one sensor is an optical sensor measuring over an area.
 19. Theprocessing system as recited in claim 15 wherein the processing systemis a vehicle processing system.